The present invention relates to a method and apparatus for removing suspended matter from liquid. The method and apparatus of the present invention have utility, for example, in separating suspended contaminants and/or oil from water.
Even more specifically, the present invention relates to a method and apparatus, wherein small bubbles created by the air injection into the main body of liquid attach themselves to the particles or droplets of contaminants to be removed and provide buoyancy to raise them to the surface of the liquid. The froth created on the surface of the liquid is removed from the surface, while heavy clean liquid remains below the froth level.
In many industries, including oil, paper and pulp, textile, electricity generating and food processing, there is an ever present problem of contaminated water as a by-product of various processes. In particular, water is often used to aid in the production of oil and gas on offshore platforms. This water is usually pumped into a formation in order to pump oil out. As a result, the water becomes contaminated with oil and solids encountered in the formation, and therefore, cannot be disposed of simply by dumping it into the surrounding water. Accordingly, numerous methods and systems have been devised to reduce the contaminant content in this water to a level which allows discharge of the water into the sea.
One such apparatus is disclosed in U.S. Pat. No. 4,782,789 issued on Nov. 8, 1988 for "Induced Static Flotation Cell". The device in accordance with '789 patent uses a plurality of gasification chambers which are sequentially, horizontally arranged for gradual separation of contaminants from water through mixing it with air bubbles which carry the contaminant laden froth to the top of the chambers for removal therefrom.
However, under certain conditions, especially wherein the space is restricted, it is impossible to utilize a horizontally arranged multi-cell unit. Additionally, a careful balancing of gas flow and liquid flow is required in order for the unit to successfully separate contaminants from water.
Another system of flotation separator is disclosed in U.S. Pat. No. 4,094,783 issued on June 13, 1978 for "Centrifugal Flotation Separator". The system, in accordance with '783 patent, shows the use of a circular, cylindrical vessel with a horizontal tray positioned inside the vessel near the top, with the tray having an axial opening. Air under pressure is introduced into the vessel from the top of the vessel, while contaminated fluid is introduced through a tangential pipe, under pressure, at a level below the tray.
However, there is a disadvantage of introducing air from the top of the vessel, since some portions of the contaminated liquid may escape mixing with air and merely settle on the bottom of the vessel, thus considerably reducing the quality of skim separation.
The present invention contemplates elimination of the above drawbacks associated with the known devices.